Circuit boards consisting of rigid and flexible sections are commonly used in the electronics industry to provide a reliable platform for mounting and interconnecting electronic components and circuitry. Such rigid/flex circuit boards alleviate problems associated with rigid circuit boards such as broken circuit connections due to vibrations or other mechanical stresses related to transporting and positioning of the circuit board.
During the process of manufacturing circuit boards, it is particularly useful to work with a rigid board in order to etch conductor lines and otherwise build up the circuit board. Thus, in order to produce a rigid/flex circuit board, rigid and flexible layers are commonly structured in such a way as to form a preparatory rigid composite which may be processed to form a unitary multilayer circuit board comprising both rigid and flexible sections. Typically, such multilayer rigid/flex circuit boards are produced by laminating a superstructure comprising rigid insulative boards to a substrate comprising individual flexible layers such that the superstructure forms the outermost layers of a rigid laminate composite. Subsequently selective portions of the rigid superstructure are severed and removed from the laminate composite to expose selective areas of the flexible substrate. These areas of exposed flexible substrate form sections of the exterior surface of the finished multilayer circuit board which are, by definition, flexible relative to the areas of the laminate composite comprised of both flexible and rigid layers.
Various methods have been disclosed to facilitate the described process of severing and removing selective portions of a rigid external layer in a laminate composite comprising rigid and flexible layers to produce a unitary rigid/flex circuit board. For example, U.S. Pat. No. 4,338,149 discloses a method in which a rigid layer is pre-cut along lines defining the area which is to be flexible in the finished circuit board. In that patent, the pre-cut rigid layer is laminated between a flexible substrate on one side and a support layer on the other side and the final rigid/flex circuit board is formed by severing the support layer along the pre-cut lines of the underlying rigid layer, subsequently removing the combination of the pre-cut portion of the rigid layer and the severed support layer.
The pre-cutting procedure of the prior art involves extra manufacturing processes which are tedious and time-consuming. In order to produce the original rigid circuit board, the manufacturer must initially provide a pre-cut rigid layer for lamination between a flexible substrate and a superfluous support layer. After the rigid circuit board including the pre-cut underlying layer is produced, an additional cutting step, which may be accomplished by the use of a laser, must be undertaken to sever the support layer at a position corresponding to the cuts in the underlying rigid layer in order to ultimately remove the rigid layer from the rigid laminate composite and to create a flexible section on the finished multilayer circuit board.
Previous inventions have suggested that laser technology could be useful in the manufacture of printed circuit boards. For example, U.S. Pat. No. 4,631,100 discloses a method for using a laser to open undesired conductive interconnects for forming predetermined circuit patterns on printed circuit boards. Likewise, U.S. Pat. No. 4,426,773 also contemplates the use of a laser to isolate electrically conductive traces. In yet another invention related to the fabrication of printed circuit boards (U.S. Pat. No. 4,417,393), a laser is used to form channels in dielectric and/or insulative substrates for creating conductive paths therein. Indeed, the use of a laser is contemplated for cutting the support layer of previously referenced U.S. Pat. No. 4,338,149 to produce rigid/flex circuit boards. The present invention provides a novel method for using a laser in conjunction with specially configured strips of laser reflective material to produce rigid/flex circuit boards.